LinkAuth method 1 is the one where we pull the TLS master secrets
out of the OpenSSL data structures and authenticate them with
RSA. Right now we list method 1 as required for clients and relays.
That's a problem, since we can't reasonably support it with NSS. So
let's remove it as a requirement and a recommendation.

As for method 3: I'd like to recommend it it, but that would make
0.2.9 start warning.  Let's not do that till at least some time
after 0.3.5 (the next LTS) is stable.

Closes ticket 27286

teor authored Aug 25, 2018 and Nick Mathewson committed Aug 24, 2018

Diagnostics for 27236.

teor authored Aug 25, 2018 and Nick Mathewson committed Aug 24, 2018

This fix requires chutney's 27230 fix to bridge client bootstrap.

Part of 27236.

Instead, count exits as usable if they have the exit flag, and
present if they also have a non-reject exit policy.

Requiring a threshold of usable descriptors avoids directories trickling
exit descriptors to clients to discover their ExitNodes settings.

Part of 27236.

Part of 26979.

Closes 26979.

To avoid future duplicates.

Part of 26979.

Part of 26979.

Part of 26979.

That's what git does for tor.

Part of 26979.

Part of 26979.

Implements 27275.

test.c no longer uses lround(), so we don't need to declare it,
and we can use math.h for fabs().

Fixes bug 27185; bugfix on 0.2.2.2-alpha.

Previously, Tor would only check the exit flag. In small networks, Tor
could bootstrap once it received a consensus with exits, without fetching
the new descriptors for those exits.

After bootstrap, Tor delays descriptor fetches, leading to failures in
fast networks like chutney.

Fixes 27236; bugfix on 0.2.6.3-alpha.